What does 300×250 – Medium Rectangle look like?
An Medium Rectangle is a display ad unit that is 300 pixels wide by 250 pixels tall. It is commonly called a 300×250 or a Med Rec, MREC, or Medium Rectangle. Right is a live example of this ad unit.
MRECs are the most popular ad unit in online advertising. This is because they typically perform best for advertisers, and therefore earn the most for websites.
300x250s are also highly versatile, being one of the only ad units to look good on both desktop and mobile phone screens. Because of this great performance and versatility you see them all over the web, which increases advertisers willingness to invest in them.
300×250 Advice for Inventory Owners
If you were to only have one ad size on your site, it should be an MREC. This is because you can generally expect the highest RPM for this ad unit (followed by the 728×90), especially if you position it above the fold.
MRECs are widely used and perform well. The fact that so many advertisers use them drives up competition for them and makes them the most essential display advertising size.
300×250 Advice for Media Buyers
The 300×250 is usually the best performing display advertising unit available. It is, therefore, also the most expensive. You can use this ad unit for almost anything, however, which makes it a vital part of any display advertising buy.
As this unit is so common across the internet, it can be used in both high and low performance placements on the same website.